U.S. patent application number 12/800931 was filed with the patent office on 2010-09-23 for electric power steering.
This patent application is currently assigned to ZF Lenksysteme GmbH. Invention is credited to Juergen Hoersh, Andreas Kruttschnitt, Jochen Nussbaumer, Wolfgang Runge, Arthur Rupp.
Application Number | 20100236860 12/800931 |
Document ID | / |
Family ID | 40821939 |
Filed Date | 2010-09-23 |
United States Patent
Application |
20100236860 |
Kind Code |
A1 |
Hoersh; Juergen ; et
al. |
September 23, 2010 |
Electric power steering
Abstract
An electric power steering system, and in particular a
power-assisted steering system for a vehicle, comprises a steering
transmission housing and a housing cover which forms an axial
closure of the steering transmission housing and which is
penetrated by an axially displaceable component of the steering
transmission. In order to provide an electric power steering system
which is easy to assemble and is not susceptible to wear, in an
axially outer region of the housing cover, a first guide bushing
for the axially displaceable component is integrated in the housing
cover.
Inventors: |
Hoersh; Juergen; (Gschwend,
DE) ; Rupp; Arthur; (Huettlingen, DE) ;
Kruttschnitt; Andreas; (Hoidenheim, DE) ; Nussbaumer;
Jochen; (Waldstetten, DE) ; Runge; Wolfgang;
(Ravensburg, DE) |
Correspondence
Address: |
JORDAN AND HAMBURG LLP
122 EAST 42ND STREET, SUITE 4000
NEW YORK
NY
10168
US
|
Assignee: |
ZF Lenksysteme GmbH
Schwaebisch Gmuend
DE
|
Family ID: |
40821939 |
Appl. No.: |
12/800931 |
Filed: |
May 26, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/EP09/00555 |
Jan 29, 2009 |
|
|
|
12800931 |
|
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Current U.S.
Class: |
180/444 |
Current CPC
Class: |
B62D 3/12 20130101; B62D
5/0448 20130101 |
Class at
Publication: |
180/444 |
International
Class: |
B62D 5/04 20060101
B62D005/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 1, 2008 |
DE |
10 2008 000 213.5 |
Claims
1. An electric power steering system, comprising a steering
transmission housing and a housing cover which forms an axial
closure of the steering transmission housing and which is
penetrated by an axially displaceable component of the steering
transmission wherein, in an axially outer region of the housing
cover, a first guide bushing for the axially displaceable component
is integrated in the housing cover, a second guide bushing is
arranged at an axial distance from the first guide bushing, and the
cross-sectional profile of the first and/or second guide bushing is
formed in such a way that a linear contact of the axially displace
able component is possible.
2. The electric power steering system according to claim 1, wherein
the first guide bushing is cast with the housing cover as an insert
in a casting mold for the housing cover.
3. The electric power steering system according to claim 1, wherein
the second guide bushing, arranged at an axial distance from the
first guide bushing is integrated in the housing cover and/or in
the steering transmission housing.
4. The electric power steering system according to claim 1, wherein
the first and/or second guide bushing is formed in one piece.
5. The electric power steering system according to claim 1, wherein
the first guide bushing forms an axial stop for the axially
displaceable component.
6. The electric power steering system according to claim 1, wherein
the ratio of the guide diameter to the width of the first and/or
second guide bushing is 0.3 to 3.5.
7. The electric power steering system according to claim 1, wherein
the ratio of the wall thickness (W) to the outer diameter (D.sub.A)
of the first and/or second guide bushing is 0.01 to 0.3.
8. (canceled)
9. The electric power steering system according to claim 1, wherein
the first and/or second guide bushing is mounted in a radially
elastic manner.
10. The electric power steering system according claim 1, wherein
the first and/or second guide bushing is disposed in the housing
cover and/or in the steering transmission housing in a manner such
that it can be positioned and fixed in the radial direction
relative to the axially displaceable component.
11. The electric power steering system according to claim 10,
wherein the first and/or second guide bushing is positioned by
means of a device for fixing the radial position.
12. The electric power steering system according to claim 11,
wherein the device for fixing the radial position comprises at
least three adjusting screws which act in the radial direction on
the first and/or second guide bushing.
13. The electric power steering system according to claim 12,
wherein the device comprises one or more eccentrics.
14. The electric power steering system according to claim 1,
wherein the first and/or second guide bushing is clamped by screws,
or riveted, or caulked, or welded or adhesively bonded in the
housing cover and/or in the steering transmission housing.
15. The electric power steering system according to claim 1,
wherein means defining a cavity arranged radially around the first
and/or second guide bushing between the first and/or second guide
bushing and the housing cover and/or in the steering transmission
housing, is filled with an elastically or non-elastically
solidifying compound.
16. The electric power steering system according to claim 1,
wherein the first and/or second guide bushing has guide surfaces
for the axially displaceable component which prevent the axially
displaceable component from rotating.
17. The electric power steering system according to claim 1,
wherein in the circumferential direction of the outer surfaces
thereof, the first and/or second guide bushing allows linear
bearing of the axially displaceable component against the first
and/or second guide bushing and/or linear bearing of the first
and/or second guide bushing against the housing cover or steering
transmission housing.
18. The electric power steering system according to claim 17,
wherein the first and/or second guide bushing is formed in a
rounded manner.
19. The electric power steering system according to claim 1,
wherein the axially displaceable component is driven by an electric
servomotor via a recirculating ball gear and a tip circle of the
recirculating ball gear is shaped in such a way that the latter
serves as a the radial bearing of the axially displaceable
component.
20. The electric power steering system according to claim 1,
wherein the first and/or second guide bushing is permanently
lubricated and/or has lubricating grooves and/or lubricating
pockets.
21. The electric power steering system according to claim 1,
wherein the first and/or second guide bushing is formed from
plastic, or from a composite material comprising metal and plastic,
or from metal.
22. The electric power steering system according to claim 1,
wherein one guide bushing is arranged at each axial end of the
steering transmission housing.
23. The electric power steering system according to claim 1,
wherein the electric power steering system is used in a power
assisted steering system for a vehicle.
Description
[0001] This is a Continuation of U.S. National Stage of
PCT/EP2009/000555 filed Jan. 29, 2009.
[0002] The invention relates to an electric power steering system,
and in particular to a power-assisted steering system for a
vehicle.
BACKGROUND OF THE INVENTION
[0003] DE 21 58594 describes a power-assisted steering system for a
vehicle, comprising a steering transmission, in the steering
transmission housing of which, an axially displaceable component
designed as a rack is guided. The rack is borne radially in the
steering transmission housing by a guide bushing, the guide bushing
being capable of compensating for bending of the rack by means of
an angular offset. The suspension of the guide bushing in the
steering transmission housing is complicated. The guide bushing is
supported radially by means of a fixed collar in a receiving bore
of a fitting which closes the steering transmission housing. In
this case, a rubber sleeve vulcanized onto the guide bushing is
pressed by the outer surface, which in part runs conically and in
part is provided with longitudinal grooves, into the receiving bore
in such a way that the guide bushing, on one hand bears axially
with its collar against a shoulder of the receiving bore, and in so
doing axially secures a sealing ring which is disposed at the end
of the receiving bore and seals off the rack, and on the other hand
is secured by a disc which is fixed between a cylindrical tube and
the fitting.
[0004] Similarly complicated radial guides for racks are known in
the case of electric power steering systems.
SUMMARY OF THE INVENTION
[0005] The object of the invention is to provide an electric power
steering system which is easy to assemble, which is not susceptible
to wear, and which operates in a trouble-free manner.
[0006] Easy assembly of the electric power steering system is
achieved by a first guide bushing for the axially displaceable
component being integrated in advance, not into a steering
transmission housing, but rather into a housing cover which axially
closes this, and which is preferably fitted last, in the assembly
of the steering transmission.
[0007] In one particularly preferred embodiment, the guide bushing
is inserted as an insert in the manner of a core, for example, into
a mold for the housing cover and is fixed in the housing cover by
way of positive fitting and/or material bonding during casting of
the housing cover.
[0008] A second guide bushing can be arranged in the housing cover
and/or in the steering transmission housing, in the same manner, or
differently. The guide bushings are preferably formed in one piece
and have an axial stop function for the rack.
[0009] Preferably, the ratio of the guide diameter to the width of
the guide bushing for the first and/or second guide bushing is
between 0.3 and 3.5. Furthermore, the ratio of the wall thickness
of the first and/or second guide bushing to the outer diameter
thereof is preferably selected at 0.01 to 0.3, in order to avoid
any jamming of the rack in the event of bending.
[0010] The axially displaceable component in the guide bushing may
be guided in a linear guide by suitably choosing the
cross-sectional profile of the guide bushing. A polygonal profile
or a design wherein the guide bushing is a roller bearing is
suitable for this. The tolerances for the diameter of the rack can
thus be compensated within certain ranges.
[0011] It may be advantageous to mount the guide bushing in a
radially elastic manner in the housing cover and/or in the steering
transmission housing, or to mount it in the housing cover or the
steering transmission housing with play, such that, under load, the
guide bushing bears against the housing cover or the steering
transmission housing.
[0012] The guide bushings can also be axially positioned and fixed,
and in particular a device for adjusting and fixing the radial
position in the housing cover or the steering transmission housing
can be used, which consists, for example, of three adjusting screws
tangentially spaced apart relative to the outer surface of the
guide bushings, and which can define the radial position of the
guide bushings in the housing cover. Eccentrics, double eccentrics
and the like are also suitable as adjusting elements that serve as
alternatives to screws. After positioning, the guide bushings can
be clamped by screws or riveted, caulked, welded or adhesively
bonded. A cavity between the outer surface of the guide bushings
and the housing cover, in the radial direction, is suitable for
introducing a compound which condenses or polymerizes
elastomerically or a solidifying compound, in order to finally fix
the guide bushings radially and axially. Preferably, the guide
surfaces of the first and/or second guide bushing are shaped in
such a way that they have a cross-sectional profile differing from
a circular shape, so that they prevent the axially displaceable
component from rotating. Moreover, the cross-sectional profile of
the outer or inner surfaces of the guide bushings may be configured
in such a way as to achieve linear bearing of the axially
displaceable component against the respective guide bushing, or
linear bearing of the guide bushing against the housing cover or
steering transmission housing.
[0013] The outer and/or inner surfaces of the guide bushings may
also be formed in a rounded manner, so that in the event of
bending, a tilted position is possible for the axially displaceable
component or the rack, and so that the guide bushing can follow the
bend line of the rack.
[0014] The electric power steering system preferably drives a
recirculating ball gear, and in particular with a view to radial
guidance in the axial region of the rack against the recirculating
ball gear, it may be advantageous if the tip circle of the
recirculating ball gear is shaped in such a way that this can be
used for radial bearing of the rack. The guide bushing in the
region of the recirculating ball gear can be mounted in a radially
elastic manner, while the guide bushing that is disposed at the end
of the housing cover can be rigidly disposed.
[0015] It may also be advantageous to configure the recirculating
ball gear in such a way that a housing therefor comprises multiple
parts and can be oriented and fixed radially. It may also be
advantageous to form the guide bushings as a passive recirculating
ball gear.
[0016] The guide bushings are permanently lubricated by means of
lubricating grooves or lubricating pockets. Suitable materials for
the guide bushings are plastic, such as polyamides,
polyoxymethylene, polyphenylene ether, polyethylene terephthalate
and polybutylene terephthalate, as well as composite materials
comprising metal and plastic or suitable bearing metals.
[0017] It may be advantageous to arrange structurally identical
guide bushings at the axial ends of the steering transmission
housing.
[0018] The invention will now be described in more detail with
reference to an exemplary embodiment and will be illustrated on the
basis of the appended drawing.
BRIEF DESCRIPTION OF THE DRAWING
[0019] FIG. 1 shows a longitudinal section through an electric
power steering system according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] FIG. 1 shows, in a longitudinal section, an electric power
steering system 1 formed as a rack-type power-assisted steering
system for a car. An axially displaceable component 4, formed as a
rack 11, is mounted in a cylindrical steering transmission housing
2 of a steering transmission 5. Parallel to the rack 11, an
electric servomotor 10 is fixed to a radial flange 12 of the
steering transmission housing 2. The rack 11 meshes at a toothed
section 13 with a pinion 14 of a steering shaft and has a thread 15
on a spindle section 16 which is engaged with a recirculating ball
thread 17 of a nut 18 of a recirculating ball gear 9. The nut 18 is
connected in a rotationally fixed manner to a toothed belt pulley
which is part of a traction gear mechanism accommodated in the
region of the radial flange 12. A radial bearing 19 for the nut 18
is held in a cylindrically shaped housing cover 3 which is
approximately the same length.
[0021] In an axially outer region 6 of the housing cover 3, which
is formed in one piece as a light metal cast part, a first guide
bushing 7 is integrated in the housing cover 3. The guide bushing 7
serves as a radial guide for the rack 11 and is formed in a
cylindrical manner, with a collar 20. The guide bushing 7 is placed
in a mold as an insert 8, made from metal, and light metal which
forms the housing cover 3 is poured around it so that it is
connected to the housing cover 3 by way of positive fitting and is
integrated therewith.
[0022] The guide diameter D is selected so that the ratio with
respect to the width b of the guide bushing 7 is approximately 0.3
to 3.5. The wall thickness of the guide bushing 7 is selected so
that the ratio with respect to the outer diameter D.sub.A thereof
is between 0.01 and 0.3. This guide bushing can quickly joined with
the housing cover 3 and adjusted by means of the housing cover 3 on
the radial flange 12, without necessitating any complicated
assembly or adjustment of the guide bushing 7.
* * * * *